By using a fine processing technology and by forming a fine flow path or a circuit on a silicone or glass substrate, equipment called the micro-analysis chip μTAS (Micro Total Analysis Systems) which conducts, in a minute space, a chemical reaction, separation, analysis of liquid samples, such as nucleic acid, protein, and blood, have been put in practical use. As an advantage of such a microchip, the amount of a sample or reagent used or the amount of discharge of waste fluid is reduced, and realization of a cheap, portable and space-saving system can be considered. A microchip is manufactured by binding two components, on at least one of which the micro-fabrication is performed.
In conventional arts, a glass substrate is used for a microchip and the various micro-fabrication methods are proposed. For example, there is the photoresist method as a method of forming a fine flow path on the surface of a glass substrate (for example, patent document 1). However, a glass substrate is not fit for a mass production method, and since its cost is very high, development of the microchip made of resin, which is cheap and disposable, is desired.
Further, there is a method of forming a fine flow path on a substrate of PDMS (polydimethylsiloxane) by the optical lithography method (for example, patent document 2). There is an advantage that edges remain (the edge or corner of a fine flow path does not become dull) in the fine flow path formed by the optical lithography method. However, by the optical lithography method, the microchip cost is high.
There is a method of forming a fine flow path in a plate-shaped substrate by the injection-molding method, which reduces the cost of a microchip, which is a major goal. This injection-molding method requires high transferability of the fine flow path for leaving edges of fine flow paths by making molding pressure high and ejection speed fast, for example. If trying to attain high transferability, the mold release resistance will become large and the release of a mold will become difficult. If the release of mold is carried out by force, distortion will remain in the joint surface on which the fine flow path has been formed. Moreover, when the mold release resistance becomes large, the form of a fine flow path changes at the time of the mold release. Furthermore, the flatness of the joint surface of the substrate is reduced by the undulation or curvature which is generated at the time of the mold release. The flatness demanded for the joint surface is 10 μm or less, for example.
Especially in injection molding of the substrate made of resin having one or more through-holes (wells) for introducing a sample or a reagent into a fine flow path, the wall of a through-hole adheres to a die by contraction of resin after molding. Thereby, mold release resistance of a through-hole becomes large. Therefore, near the through-hole, change of the form of the fine flow path is marked, and there is a tendency for the flatness of the substrate to be also reduced markedly.
In a substrate where a cylindrical part (chimney) is provided to protrude to the opposite side from the joint surface of the substrate, on the opposite surface to the joint surface and where a through-hole is prepared in the center of the cylindrical part, the area where the wall of the through-hole adhering to the die increases and mold release resistance of the through-hole becomes still larger, by contraction of resin after molding. Therefore, the tendency changing the form of a fine flow path and reduction of the flatness of the substrate becomes extremely marked near the through-hole.
Generally for a joint of resin materials, adhesives, such as glue, are used. In the joint using an adhesive, the adhesive layer has a certain amount of thickness, and does double duty as a shock absorbing material. Therefore, it is not often the case that distortion and flatness of an adhesion side influence the joint's properties.
However, the substance which may have influence on the analysis cannot be allowed to be placed between the joint surfaces of a substrate in the microchip made by joining a covering material. Therefore, direct joint of the substrate and a covering material based on a joint using heat is required.
Experiments showed that the distortion and reduction of flatness of a joint surface influences joint accuracy and quality greatly in a jointing process using heat.
When a covering material is joined to the joint surface of a substrate using heat, the distortion and reduction of flatness of a joint surface reduces the joint's strength of the substrate and the covering material. Then, the sealing property of a fine flow path or a through-hole is reduced, and air contamination (air retention) on the joint surface occurs. It generates and has large influence on the joint accuracy and quality of the microchip.
In conventional injection-molding methods, as a technology for separating the mold, which is a substrate, from a die, there is a method of separation from a die 2 by pushing an empty area of a substrate 1 by the ejector pins 3, as shown in FIG. 8. Further, as shown in FIG. 9, there is a method of separation from a die 2 by pushing out the taper-shaped peripheral wall 4 of the substrate 1 by the ejector pins 3. Furthermore, as shown in FIG. 10, there is a method of pushing out the taper-shaped peripheral wall 4 and the peripheral edges 5 of the substrate 1 by the ejector pins 3, each having a step. Furthermore, as shown in FIG. 11, there is a method of pushing out the entire surface 6 of the substrate 1 by a block 7.    [Patent document 1] Unexamined Japanese Patent Application Publication No. 2003-215140    [Patent document 2] Unexamined Japanese Patent Application Publication No. 2006-53064